Currently, in companies, along with the increase of data amount, storage systems are becoming larger in scale and complexity. Therefore, companies demand simplifying the management and improving the use efficiency of storage apparatuses. One of the technologies for satisfying this demand is Thin Provisioning. This is the technology in which a storage system provides a virtual logical volume which does not comprise a physical storage area (hereinafter referred to as a virtual volume) to a host computer and, in accordance with the write from the host computer to the virtual volume, dynamically assigns pages from a pool. At this point, a “pool” is a set of multiple pages, and a “page” is a physical storage area.
By this technology, the capacity of the storage system can be made more efficient and the capacity design can be simplified.
Generally, a pool is configured of media (a page group) of the same performance. However, usually, the access frequencies of multiple pages assigned to a virtual volume are not the same, and there are some cases in which, in those multiple pages, pages with high access frequencies and pages with low access frequencies are mixed. Therefore, excess or deficiency of the performance might occur. As more specifically described, for example, if a pool is configured only of high-performance media, excessive performance occurs in the pages whose access frequencies are low while, if a pool is configured only of low-performance media, performance deficiency occurs in the pages whose access frequencies are high.
As a method for solving the problem, the method described in the Patent Literature 1 can be considered. According to the Patent Literature 1, one pool is configured of multiple media of different performances, and data in a page is reallocated from the medium comprising the page to the medium which is the optimum for the access frequency of the page.